Field of the Invention
The present invention relates to a non-reciprocal circuit device and a communication apparatus using the same and, more particularly, to a non-reciprocal circuit device of a distributed constant type and a communication apparatus using the same.
Description of Related Art
A non-reciprocal circuit device such as an isolator or a circulator is incorporated in, for example, a mobile communication apparatus like a mobile phone or a communication apparatus used in a base station. The non-reciprocal circuit devices can be classified into a distribution constant type, a concentrated constant type, and the like. Among them, the non-reciprocal circuit device of the distribution constant type is suitable for use in a base station and the like where high power output signal is required.
A structure of the distribution constant type non-reciprocal circuit device is described in, e.g., Japanese Patent Application Laid-Open No. 1997-121104. The non-reciprocal circuit device described in Japanese Patent Application Laid-Open No. 1997-121104 has a center conductor including three conductors (main conductor portions) extending radially at an angular interval of 120° and three electrode portions (branched conductor portions) extending radially from the roots of the main conductor portions at an angular interval of 120°. This center conductor is placed on a substrate. The substrate is an integrated substrate made up of a ferrite plate in disk shape and a dielectric ring surrounding the ferrite. A leading end of each of the three main conductor portions is connected to an input/output terminal or a terminal resistor, whereby a signal is input/output or terminated. The three branched conductor portions are designed to have such a shape and a size as to obtain intended high-frequency characteristics (e.g., capacitance).
In the non-reciprocal circuit device described in Japanese Patent Application Laid-Open No. 1997-121104, the leading ends of the respective main conductor portions are expanded in a peripheral direction, and the expanded portions cover the dielectric ring. In Japanese Patent Application Laid-Open No. 1997-121104, a width of each of the expanded portions in the radial direction is substantially equal to a width of the dielectric ring in the radial direction. Thus, if a displacement occurs in amounting position of the center conductor, a change in the high-frequency characteristics becomes very large.
That is, if a displacement occurs in the mounting position of the center conductor, a difference in condition occurs among the three main conductor portions. That is, the expanded portion of a given main conductor portion is overlapped on the disk-shaped ferrite plate, while the expanded portion of another main conductor is not overlapped with the disk-shaped ferrite plate, with the result that the high-frequency characteristics may change significantly.